Problem: If $5a + 3b + c = -9$ and $5x + 6y = 4$, what is $-24b - 25x - 30y - 40a - 8c$ ?
Explanation: $= -40a - 24b - 8c - 25x - 30y$ $= (-8) \cdot (5a + 3b + c) + (-5) \cdot (5x + 6y)$ $= (-8) \cdot (-9) + (-5) \cdot (4)$ $= 72 - 20$ $= 52$